<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
  <style>
    #box {
      padding: 20px;
      background: palegoldenrod;
    }
  </style>
</head>
<body>
  <!-- <div id="box"></div>
  <button id="btn1">执行计算任务</button>
  <button id="btn2">更改背景颜色</button>
<script>
  const box = document.getElementById('box')
  const btn1 = document.getElementById('btn1')
  const btn2 = document.getElementById('btn2')

  let number = 999999
  let value = 0

  function calc() {
    while (number > 0) {
      value = Math.random() < 0.5 ? Math.random() : Math.random()
      console.log(value)
      number--
    }
  }

  btn1.onclick = function () {
    calc()
  }

  btn2.onclick = function () {
    box.style.background = 'green'
  }
</script> -->
  <div id="box"></div>
  <button id="btn1">执行计算任务</button>
  <button id="btn2">更改背景颜色</button>
  <script>
    const box = document.getElementById('box')
    const btn1 = document.getElementById('btn1')
    const btn2 = document.getElementById('btn2')

    let number = 999999
    let value = 0

    function calc(deadline) {
      while (number > 0 && deadline.timeRemaining() > 0) {
        value = Math.random() < 0.5 ? Math.random() : Math.random()
        console.log(value)
        number--
      }
      requestIdleCallback(calc)
    }

    btn1.onclick = function () {
      requestIdleCallback(calc)
    }

    btn2.onclick = function () {
      box.style.background = 'green'
    }
  </script>
</body>
</html>